1. Technical Field
Example embodiments relate to repairing, and more particularly to redundancy circuits, semiconductor memory devices including the same and methods of repairing a semiconductor memory device.
2. Description of the Related Art
As the integration degree of a semiconductor memory increases, a capacity of the semiconductor memory is increasing rapidly. Increasing of the capacity of the semiconductor memory according to the development of the semiconductor technology represents that the number of memory cell included in a chip increases. As the number of memory cell increases, the number of the defective memory cell also increases. Since an existence of a single defective memory cell causes a critical problem in the semiconductor memory device, redundant memory cells are provided against the defective memory cells. The defective memory cells are replaced with the redundant memory cells based on fuse information. When an address of the defective memory cell is inputted, a normal path is cut off and a redundancy path to the redundant cell is activated according to programmed/unprogrammed state of the fuse.
A laser fuse, as one of the widely used fuses, is programmed by cutting the fuse formed with a metal line using laser beam. The laser fuse has an advantage of being simply embodied since an additional circuit to control cutting of the fuse is unnecessary. The laser fuse, however, has disadvantages of limitation to the integration density regardless of the development of the semiconductor memory manufacturing process technology, such as a metal oxide semiconductor (MOS) process, since a predetermined interval between the fuses has to be secured to prevent damages due to laser fusing. Furthermore the laser fuse can not be reprogrammed after the memory chip including the fuse circuit is packaged. To overcome these disadvantages, an electrical fuse and an anti-fuse programmed by using an electrical signal have been proposed. These fuses have advantages that they can be reprogrammed even after the memory chip is packaged since they are activated or deactivated by the electrical signal. In addition, the size of the fuse circuit may be reduced as the scale of the manufacturing process is reduced. However, in the electrical fuse, residues remain around cutting area and thus the resistance of the program unit may not increase sufficiently. Such residues form an electrical path having a finite resistance. In the anti-fuse, electrical short may be incomplete and thus the resistance of the program unit may not decrease sufficiently. In these cases of incomplete programming, the change of the resistance of the program units is not sufficient and it is indefinite whether or not the program unit is programmed, thereby degrading the reliability of the fuse circuit.
The electrical fuse is programmed (i.e. cut) by applying a relatively high current through the electrical fuse in response to a control signal. The electrical fuse can be cut by externally applying the control signal even after the fuse circuit is packaged. The electrical fuse, however, requires a large size of a control driver for applying a high current through the electrical fuse and thus the size of the fuse circuit is relatively large.
The anti-fuse is programmed (i.e., electrically shorted) by applying a relatively high voltage to the anti-fuse in response to the control signal. Generally, the anti-fuse is embodied by a capacitor and both ends of the capacitor are electrically connected when dielectric material in the capacitor is damaged by the applied high voltage. The anti-fuse can be programmed by externally applying the control signal even after the fuse circuit is packaged. The reliability of the anti-fuse is determined according to a level of the applied voltage and thus the anti-fuse needs high voltage for increasing the reliability.
As such, the electrical fuse and the anti-fuse have advantages but they have a common disadvantage that the reliability of them is lower than the laser fuse since electrical characteristic of such fuses may be varied according to the change of manufacturing process. To increase the reliability of the electrical fuse and the anti-fuse, various methods are proposed but conventional methods can not guarantee the reliability of the fuses.